Optical disk reproducing devices have remarkably improved in recording/reproducing speed in recent years. The improvement in recording/reproducing speed has been achieved by increasing the rotational speeds of optical disks.
However, when an optical disk is increased in rotational speed, a vibration caused by mass eccentricity of the optical disk adversely affects the control of a servo and so on, resulting in inconvenience on the user of an optical disk reproducing device.
In order to prevent such adverse effect of a vibration caused by a disc of large mass eccentricity, when the disk of large mass eccentricity is loaded, an optical disk reproducing device controls the rotary driving of an optical disk so as to limit the rotational speed of the optical disk.
The vibration amplitude caused by the disk is measured during the control. The measurement is a significant technique for preventing the adverse effect of a vibration caused by the disk of large eccentricity in the optical disk reproducing device. Particularly a vibration detecting technique using a track count is known as an inexpensive detecting method not demanding additional cost for the installation of a vibration sensor or the like which directly detects a mechanical vibration.
As described above, the conventional optical disk reproducing device which uses a track count to detect a vibration will be described below. An optical disk reproducing device of Japanese Patent Laid-Open No. 2000-113581 will be discussed as an example.
FIG. 9 is a block diagram showing the configuration of a conventional optical disk reproducing device for detecting a vibration using a track count. In FIG. 9, reference numeral 900 denotes an optical disk reproducing device, reference numeral 801 denotes a base, reference numeral 802 denotes a disk motor fixed on the base 801, reference numeral 803 denotes insulators for supporting the base 801, reference numeral 804 denotes a disk to be reproduced that is mounted on the disk motor 802, reference numeral 901 denotes an optical head, reference numeral 902 denotes an elastic member for suspending the optical head 901 from the base 801, reference numeral 903 denotes a light beam which is incident on the optical disk 804 from the optical head 901, reference numeral 904 denotes information recording tracks which are formed like concentric circles or spirals with constant pitches on an information recording surface 804A of the disk 804, reference numeral 905 denotes a track cross detecting section which generates a track cross pulse and a cross signal from a signal reproduced when the light beam 903 traverses the information recording tracks 904, reference numeral 906 denotes a counting section for counting the track cross pulses, reference numeral 907 denotes a measuring section for deciding a quantity of mass eccentricity based on the counting result of the counting section 906, and reference numeral 908 denotes a motor control section which controls the number of rotations of the disk motor 802 and outputs rotation angle information to the measuring section 907.
Regarding the conventional optical disk reproducing device configured thus, a vibration detecting operation will be described below.
First, in the optical disk reproducing device 900, the optical head 901 is kept at a fixed distance from the disk 804 so that the focus of the optical beam 903 is positioned on the information recording surface 804A of the disk 804. The relative position of the optical head 901 to the disk 804 in the radius direction (the direction of arrow R) of the disk 804 has a vibration characteristic indicated by a natural frequency foA, which is determined by the mass of optical head 901 and the spring constant of the elastic member 902 made of a material such as a metal, a resin, and a rubber.
The base 801 is supported by the insulators 803 made of a material such as a metal, a resin, and a rubber. When centrifugal force generated by the rotation of the disk 804 is propagated to the base 801 through the disk motor 802, the base 801 is vibrated according to a characteristic indicated by a natural frequency foM, which is determined by the spring constant of the insulators 803 and the mass of all the constituent elements including the base 801, the optical head 901, the disk motor 802, and the disk 804 that are mounted on the base 801.
The motor control section 908 rotates the disk motor 802 at a first rpm (low-speed rotation) sufficiently lower than the natural frequency foA. The optical disk 804 mounted on the disk motor 802 rotates at the first rpm.
At the first rpm sufficiently lower than the natural frequency foA, the optical head 901 is vibrated integrally with the base 801. The relative positions of the optical head 901 and the optical disk 804 hardly change. Hence, at the first rpm sufficiently lower than the natural frequency foA, the light beam 903 traverses the information tracks 904. The number of the information recording tracks 904 corresponds to an eccentricity amount thereof. The light beam 903 generates a track cross corresponding to the number of the information recording tracks 904.
Based on the reproduction signal of the optical head 901, the track cross detecting section 905 detects the track cross corresponding to the number of the information recording tracks 905 traversed by the light beam 903. The track cross detecting section 905 generates a track cross pulse corresponding to the detected track cross. The track cross detection section 905 outputs the generated track cross pulse to the counting section 906.
The counting section 906 counts track cross pulses of one rotation of the disk 804 based on rotation angle information from the motor control section 908. The measuring section 907 stores, as N1(0) to N1 (n−1), the counting result of track cross pulses of one rotation of the disk 804 which is counted by the counting section 906 for each area obtained by dividing one rotation into n.
Subsequently, the motor control section 908 rotates the disk motor 802 at a second rpm (high-speed rotation) which is higher than the natural frequency foA and is lower than the natural frequency foM. The mass eccentricity of the disk 804 generates centrifugal force on the disk 804. The base 801 is vibrated according to amplitude determined by the spring constant of the insulators 803, the mass eccentricity amount of the disk 804, the mass of all the constituent elements mounted on the base 801.
When the disk motor 802 is rotated at the second rpm which is higher than the natural frequency foA and lower than the natural frequency foM, only the base 801, the disk motor 802, and the disk 804 are integrally vibrated and the optical head 901 is made stationary. Hence, a relative displacement between the disk 804 and the optical head 901 is equal to the vibration displacement of the base 801. As a result, the light beam 903 generates a track cross having the number of tracks corresponding to the sum of the eccentricity amount of the information recording track 904 and the vibration amplitude of the base 801.
Based on the reproduction signal of the optical head 901, the track cross detecting section 905 detects a track cross corresponding to the number of tracks which are equivalent to the sum of the eccentricity amount of the information recording track 904 and the vibration amplitude of the base 801. The track cross detecting section 905 generates a track cross pulse corresponding to the number of tracks which are equivalent to the sum of the eccentricity amount of the information recording track 904 and the vibration amplitude of the base 801. The track cross detecting section 905 outputs generated track cross pulse to the counting section 906.
The counting section 906 counts a track cross pulse of one rotation of the disk 804 based on rotation angle information from the motor control section 908. The measuring section 907 performs an operation to obtain the vibration amplitude of the base 801 after subtracting count results N1(1) to N1(n) from count results N2(1) to N2(n) counted by the measuring section 906.
To be specific, the vibration amplitude is obtained by the equation below.
                                                                        dat                ⁢                                                                  [                1                ]                            =                                                N1                  ⁡                                      (                    1                    )                                                  -                                  N2                  ⁡                                      (                    1                    )                                                                                                                                          dat                ⁢                                                                  [                2                ]                            =                                                N1                  ⁡                                      (                    2                    )                                                  -                                  N2                  ⁡                                      (                    2                    )                                                                                                            ⋮                                                                              dat                ⁢                                                                  [                n                ]                            =                                                N1                  ⁡                                      (                    n                    )                                                  -                                  N2                  ⁡                                      (                    n                    )                                                                                                          (                  Equation          ⁢                                          ⁢          15                )            
For example, when n=6, the following equations are established:
                              VIBRATIN          ⁢                                          ⁢          AMPLITUDE          ⁢                                          ⁢                      1            ⁡                          [              n              ]                                      =                  2                      3                                              (                  Equation          ⁢                                          ⁢          16                )                                                                                              DAT                ⁡                                  [                  n                  ]                                            2                        +                                          DAT                ⁡                                  [                  n                  ]                                            ⁢                              DAT                ⁡                                  [                                      n                    +                    1                                    ]                                                      +                                          DAT                ⁡                                  [                                      n                    +                    1                                    ]                                            2                                                                                                              VIBRATION          ⁢                                          ⁢          AMPLITUDE          ⁢                                          ⁢                      2            ⁢                                                  [            n            ]                          =                  2                      3                                              (                  Equation          ⁢                                          ⁢          17                )                                                                                              DAT                ⁡                                  [                  n                  ]                                            2                        +                                          DAT                ⁡                                  [                  n                  ]                                            ⁢                              DAT                ⁡                                  [                                      n                    +                    2                                    ]                                                      +                                          DAT                ⁡                                  [                                      n                    +                    2                                    ]                                            2                                                                                (when n=1 to 6 and n>6, n=n−6 is established)
In an operation of a square root, since the number of program steps is ordinarily increased, a value proportionate to the square of vibration amplitude is used as a vibration detection value. Further, of track count data in an area divided into n, a vibration detection value is found only from data in two areas. Thus, an error count of one area seriously affects a detection value. In order to avoid the influence, the following method is known: 12 vibration detection values in total are calculated by (equation 16) and (equation 17), from which six values are calculated, respectively, and an average value of these plural median values or the twelve pieces of data is used as a vibration detection value.
Then, the maximum rotational speed of a disk of an optical disk device is determined by comparing the calculated vibration detection value with a threshold value.
However, in the conventional optical disk reproducing device disclosed in Japanese Patent Laid-Open No. 2000-113581, the track count result of an eccentric component measured at the first rotational speed is subtracted by arithmetic after the track count result is measured at the second rotational speed. Thereafter, it is necessary to further perform a complicated operation to obtain a vibration detection value corresponding to vibration amplitude. Thus, a value proportionate to the square of vibration amplitude is usually used as a vibration detection value. In this case, since the square of vibration amplitude is used, it is necessary to use a high-precision variable (with a large significant figure) for calculation in order to precisely control a recording/reproducing speed.
Moreover, a number of multiplications are used and the calculation is complicated, thereby increasing the number of program steps for control. For this reason, it takes a long time to calculate a vibration detection value, delaying the result. Thus, it is not possible to promptly control a recording/reproducing speed.
Therefore, it is an object of the present invention to provide an information disk recording/reproducing device and a method for controlling a recording/reproducing speed thereof whereby a recording/reproducing speed can be precisely controlled without the necessity for using a high-precision variable for computing a vibration detection value, and a vibration detection value can be promptly calculated and a recording/reproducing speed can be controlled without the necessity for an extra number of program steps.